It is the long range purpose of this project to study the control mechanisms important in regulating protein synthesis in normal and malignant lymphoid cells. The organization of immunoglobulin light and heavy chain genes and the control mechanisms in selecting those being transcribed and those which are expressed in protein synthesis are being studied. Particular attention is being given to the molecular genetics of IgD, since this molecule, along with IgM, appears to be a very important surface component of most B lymphocytes. We have prepared a cDNA clone for mouse IgD heavy chain and used it to isolate a genomic DNA clone containing both IgD and IgM heavy chain genes. The DNA sequence of both clones has been completed, and we have discovered that IgD has multiple gene segments coding for alternative carboxyl-termini for IgD that either is secreted or membrane bound. The mRNAs for these different forms of IgD heavy chain have been identified and their processing is being studied.